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  1. anubis512

    ASHRAE 15 Chiller PRV Capacity

    Thanks, that makes a lot of sense. It's always confused me, as a young engineer, that codes typically say "x is required"...and then leave the determination of x up to the user. With regards to relief valves, I understand what you've said. At the same, the API 520/521 methodology for sizing a...
  2. anubis512

    ASHRAE 15 Chiller PRV Capacity

    ...the chiller vendor for their relief valve calculations. They gave some very basic info and deferred to the ASHRAE 15, Section 9.7.5 Equation: C = f*D*L Where: C = Capacity (#/min, air) f = Refrigerant Factor D = Vessel Diameter L = Vessel Length I'm confused because ASHRAE also says pressure...
  3. anubis512

    Choked Flow Critical Area Question

    SNORGY, Thanks for the article. I've actually come across that one before and it's very helpful.
  4. anubis512

    Choked Flow Critical Area Question

    zdas, Wow. I knew compressible flow was infinitely uglier than incompressible flow but I didn't know we couldn't analyze so much of it in a pipe. This came about from not fully understanding the compressible flow software we have and trying to educate myself to hopefully explain what it was...
  5. anubis512

    Choked Flow Critical Area Question

    One last question I think. 27 psia is the pressure upstream the last shock wave, just inside the pipe. How do you determine where the other shock waves are? In other words, how do you know it doesn't just go from 14.7-> 27-> 50-> 92-> 169-> 310 psia, etc, up to 5,457, in consecutive shock...
  6. anubis512

    Choked Flow Critical Area Question

    Very interesting. How do pipe fittings factor into the pressure drop? Do you calculate their losses via traditional equivalent length methods, at the given velocity "between" shock waves? Attached is a quick sketch of the tailpipe of the scenario you described, with some fittings added. I'm...
  7. anubis512

    Choked Flow Critical Area Question

    So you start at atmospheric pressure if it's discharging to atmosphere. With k = 1.3 and Pcritical= 14.7 psia, P = 27 psia. Therefore if the pressure in your tailpipe is equal to or above 27 psia, you have a shock wave at this point? Then, in your scenario, you'd have another shock wave where...
  8. anubis512

    Choked Flow Critical Area Question

    ...be the best approach to calculate it in your opinion? I've come across some things saying the pressure in pipe after it becomes choked can't fall below P* while others seem to imply only the region directly downstream of the shock is P* and frictional losses are calculated as they usually are.
  9. anubis512

    Choked Flow Critical Area Question

    ...area A, mass flow (G) increases until it's choked. I'm having a hard time visualizing/understanding: [ol 1] Why A cannot be less than the defined A*. In the sketch I attached, what happens? Does it just mean flow isn't isentropic? Why exactly the gas cannot exceed M = 1. What's physically...
  10. anubis512

    Choked Flow Critical Area Question

    Attached is a sketch of a pipe line showing my question, I hope. If A can never be less than A*, can you explain why that is in a physical or practical sense? I'm having trouble understanding choked flow in general, so any guides or references you could point me to would be appreciated...
  11. anubis512

    Choked Flow Critical Area Question

    ...section discussing mass flow, Saad shows that the maximum mass flow occurs when Mach Number = 1 and minimum flow area. The minimum flow area is A* the cross sectional area at M = 1. He goes on to define a ratio A(actual)/A* and states that this value can never be less than 1. What does this...
  12. anubis512

    Shell & Tube HE - Tubes under External Pressure

    Hi, I'm working on a project where the shell side is rated 350/-15 psig while the tube side is rated 200/-15 psig. In my mind, the tubes could theoretically experience 350 psig external pressure, which is not what it's rated for. I can't seem to find very much literature on a HE where the shell...
  13. anubis512

    Latent Heat of Vaporization Equation

    Hi All, I'm trying to calculate the latent heat of vaporization of a chemical using the equation found in Perry's Chemical Handbook, Table 2-150. It gives the latent heat equation and chemical specific constants. My issue is I can't get that equation, which outputs J/kmol, to convert correctly...
  14. anubis512

    Amount of Vacuum Created from Condensing Vapor

    Hi, I'm attempting to calculate the amount of vacuum generated on a distillation column to determine if a vacuum relief device is required. Currently I'm examining two cases - 1) the condenser operating at full load while the reboiler is shut off & 2) a cold top feed collapsing the rising...
  15. anubis512

    Help Finding an Article

    If there was a way to just purchase that article, I'd be fine with that. I don't really want to subscribe though..
  16. anubis512

    Help Finding an Article

    Hi all, I'm going through relief valve calculations. In numerous forums/articles I've seen this article referenced, but I can't find it. Does anyone have a copy or know where I could find it? Wing Y. Wong - "Fires, Vessels and the Pressure Relief Valve", May 2000, pages 84-92 Thanks!
  17. anubis512

    API 521 Vapor Discharge Capacity Equation

    After further reading, I found it mentioned in text, but it wasn't in equation form. Thanks for your help
  18. anubis512

    API 521 Vapor Discharge Capacity Equation

    I understand that, but I don't see W = Q/dH in the actual standard, at least the version we have. Is it located elsewhere?
  19. anubis512

    API 521 Vapor Discharge Capacity Equation

    Hi all, I'm in the process of sizing relief valves and I have a question about the equation for vapor discharge capacity (W) found in API RP 521. We have an old copy on file (1990) and the equation for vapor discharge (A-7) is a little complicated. Looking through our Consolidated book, Crosby...
  20. anubis512

    PSV Model with sonic flow

    Thanks for the response gentlemen, I think I got my model sorted out. I didn't stop to think the placement of fittings could have such a large impact, but putting two elbows on the 4" section of piping after the area change made things much better.

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